Sales order support (#438)

* Add new models for SalesOrder

- Create generic Order and OrderLine models with common functionality

* Refactor

- Move some widgets around
- Cleanup directory structure

* Add link to home screen and nav drawer

* Add SalesOrder list widget

* Linting fixes

* Fix string

* Refactor PurchaseOrderDetailWidget

* Tweaks to existing code

* linting

* Fixes for drawer widget

* Add "detail" page for SalesOrder

* Add more tiles to SalesOrder detail

* Allow editing of salesorder

* add list filters for sales orders

* Display list of line items

* Customer updates

- Display customer icon on home screen
- Fetch sales orders for customer detail page

* Cleanup company detail view

* Create new sales order from list

* Stricter typing for formFields method

* Create new PurchaseOrder and SalesOrder from company deatil

* Status code updates

- Add function for name comparison
- Remove hard-coded values

* Update view permission checks for home widget

* Add ability to manually add SalesOrderLineItem

* Add nice progress bar widgets

* Display detail view for sales order line item

* edit SalesOrderLineItem

* Fix unused import

* Hide "shipped items" tab

- Will be added in a future update

lib/widget/part/part_suppliers.dart

@@ -0,0 +1,83 @@
+import "dart:core";
+
+import "package:inventree/l10.dart";
+
+import "package:inventree/api.dart";
+
+import "package:flutter/material.dart";
+import "package:inventree/inventree/part.dart";
+import "package:inventree/inventree/company.dart";
+import "package:inventree/widget/company/company_detail.dart";
+import "package:inventree/widget/refreshable_state.dart";
+
+class PartSupplierWidget extends StatefulWidget {
+
+  const PartSupplierWidget(this.part, {Key? key}) : super(key: key);
+
+  final InvenTreePart part;
+
+  @override
+  _PartSupplierState createState() => _PartSupplierState(part);
+
+}
+
+
+class _PartSupplierState extends RefreshableState<PartSupplierWidget> {
+
+  _PartSupplierState(this.part);
+
+  final InvenTreePart part;
+
+  List<InvenTreeSupplierPart> _supplierParts = [];
+
+  @override
+  Future<void> request(BuildContext context) async {
+    // TODO - Request list of suppliers for the part
+    await part.reload();
+    _supplierParts = await part.getSupplierParts();
+  }
+
+  @override
+  String getAppBarTitle() => L10().partSuppliers;
+
+  @override
+  List<Widget> appBarActions(BuildContext contexts) {
+    // TODO
+    return [];
+  }
+
+  Widget _supplierPartTile(BuildContext context, int index) {
+
+    InvenTreeSupplierPart _part = _supplierParts[index];
+
+    return ListTile(
+      leading: InvenTreeAPI().getThumbnail(_part.supplierImage),
+      title: Text("${_part.SKU}"),
+      subtitle: Text("${_part.manufacturerName}: ${_part.MPN}"),
+      onTap: () async {
+        var company = await InvenTreeCompany().get(_part.supplierId);
+
+        if (company != null && company is InvenTreeCompany) {
+          Navigator.push(
+              context,
+              MaterialPageRoute(
+                  builder: (context) => CompanyDetailWidget(company)
+              )
+          );
+        }
+      },
+    );
+  }
+
+  @override
+  Widget getBody(BuildContext context) {
+    return ListView.separated(
+      shrinkWrap: true,
+      physics: ClampingScrollPhysics(),
+      separatorBuilder: (_, __) => const Divider(height: 3),
+      itemCount: _supplierParts.length,
+      itemBuilder: _supplierPartTile,
+    );
+  }
+
+}